Magnetic recording media comprising a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic iron oxide particles, ferromagnetic alloy particles and binders are widely used as media of video tapes, audio tapes, and so on.
In recent years, with the strong demand for higher density recording in magnetic recording media, demands for higher vision image qualities and higher sound qualities have increased. Therefore, it has been necessary that electromagnetic properties be improved, that is, particularly that C/N (the ratio of carrier to noise) be increased and that BN (bias noise) be decreased.
For the above purposes, the size of ferromagnetic particles must be lessened and the number of magnetic particles per unit volume must be increased. However, if the specific surface area of ferromagnetic particles is increased to increase the number of magnetic particles per unit volume, voids are formed on the surface of the ferromagnetic particles and in actuality, the particle size is not so small as desired or the axis ratio of the long axis length to the short axis length becomes lower, whereby the above objects can not be fulfilled. In other words, there are some problems in that if voids are formed, loss of magnetic susceptibility increases and that if the axis length ratio of the ferromagnetic particles becomes lower, magnetic orientation of magnetic particles is not carried out effectively upon preparing a magnetic recording medium. Further, if the size of ferromagnetic particles is lessened, print-through characteristics are deteriorated due to increase of composition (particles) having low coercive force and the resulting medium can not be used practically. Furthermore, if the size of ferromagnetic particles is lessened, the light-transmission degree of a magnetic layer increases. In a video tape deck (VHS type, 8 mm type and so on), the end of a tape is detected by a photosensor capable of detecting light at about 900 nm wavelength, and therefore, the light-transmission degree of a tape needs to be 10% or less to avoid an erroneous end-of-tape operation of the photosensor. Accordingly, when the size of ferromagnetic particles is lessened, it is necessary to add light-intercepting particles into a magnetic layer in a large amount, to provide a thick backing coat layer to light-intercept if necessary, or to provide another light-intercepting layer.
However, when light-intercepting particles are added into a magnetic layer in a large amount, electromagnetic properties are deteriorated. When a backing coat layer or another light-intercepting layer is provided to intercept light, surface properties and electromagnetic properties tends to be deteriorated by the orange peel of the backing layer caused by making the layer thick.
When the size of ferromagnetic particles is increased to ensure satisfactory print through characteristics, there is a problem in that head wear-out increases.